Pyridine-N-oxides which are substituted in the 2-, 3- or 4-position with an acetyl group are known compounds. (for 2-, see Katritzky et al., Soc. 2182, 2191 (1958); for 3- and 4-, see Kanno, J. Pharm. Soc. Japan 73: 120 (1953)). Pyridine-N-oxides which are substituted in the 2-, 3- or 4-positions with various substituents are known for use in photography generally.
For instance, it is known in the art, as taught by U.S. Pat. No. 3,691,210 that pyridine-N-oxide can be used in the synthesis of dye developers such as 2-(omega-hydroquinonyl-alkyl )-anthraquinones, e.g., 2-(omega-hydroquinonyl-pentyl)-1,4-dihydroxy-5,8-bis-.alpha.-ethyl-propyla mino-anthraquinone.
Another use for pyridine-N-oxides in photography is described in U.S. Pat. No. 4,006,150 which discloses that pyridine-N-oxides substituted in the ortho and/or para position, i.e., in the 2- and/or 4-position, with an alkylsulfonylmethyl group are useful as photographic speed enhancers of the red-sensitive silver halide emulsion in dye developer diffusion transfer photographic processes and in color diffusion transfer processes, products and compositions employing the N-oxides of certain N-heterocyclicalkyl sulfones. It also discloses that, unlike the system described in U.S. Pat. No. 3,691,210 wherein the pyridine-N-oxide becomes part of the dye developer, the pyridine-N-oxides by themselves can be initially disposed in the processing composition or in a layer of the image-recording element.
U.S. Pat. No. 4,175,966 discloses a light-sensitive black and white silver halide photographic material containing a substantially non-diffusible compound having oxidation power on a hydroquinone developing agent. It also discloses typical examples of substantially non-diffusible compounds including "other organic oxidized compounds" such as pyridine-N-oxide polymer.
U.S. Pat. No. 4,203,766 discloses that pyridine-N-oxides can assist in the control of dye transfer in diffusion transfer photographic systems which utilize dye developers as the image dye-providing materials by minimizing the diffusion of oxidized dye developers. It is also disclosed that, in such systems, pyridine-N-oxides provide a beneficial solvating action for unoxidized dye developer, particularly, magenta dye developer, thereby improving transfer of unoxidized dye developer without rendering oxidized dye developer more diffusible than the dye developer would be under ordinary development conditions. It is further disclosed that, in such systems, pyridine-N-oxides which are substituted in any position(s) of the pyridine ring with a methyl group(s) can also provide improved color isolation, i.e., the transfer of the dye developers is more closely controlled by the silver halide emulsion with which each is associated. Among the compounds disclosed in U.S. Pat. No. 4,203,766 as being useful for this purpose are those which are substituted in the 2-, 3- and/or 4-position with a methyl group.
U.S. Pat. No. 4,767,698 discloses that pyridine-N-oxides can be used to prepare photographic cyan dye-releasing compounds. It also discloses that, these cyan dye-releasing compounds in the process of photographic development release diffusible cyan dyes which have improved lightfastness, improved spectral properties and improved resistance to reducing agents.
Diffusion transfer multicolor films are well known in the art. U.S. Pat. No. 2,983,606 discloses a subtractive color film which employs red-sensitive, green-sensitive and blue-sensitive silver halide layers having associated therewith, respectively, cyan, magenta and yellow dye developers. In such films, oxidation of the dye developers in exposed areas and consequent immobilization thereof has provided the mechanism for obtaining imagewise distribution of unoxidized, diffusible cyan, magenta and yellow dye developers which are transferred by diffusion to an image-receiving layer. While a dye developer itself may develop exposed silver halide, in practice the dye developer process has utilized a colorless developing agent, sometimes s referred to as an "auxiliary" developer, a "messenger" developer or an "electron transfer agent", which developing agent develops the exposed silver halide. The oxidized developing agent then participates in a redox reaction with the dye developer thereby oxidizing and immobilizing the dye developer in imagewise fashion. A well known messenger developer has been 4'-methylphenylhydroquinone. Commercial diffusion transfer photographic films of Polaroid Corporation including Polacolor SX-70, Time Zero and 600 have used cyan, magenta, and yellow dye developers.
U.S. Pat. Nos. 3,719,489 and 4,098,783 disclose diffusion transfer processes wherein a diffusible image dye is released from an immobile precursor by silver-initiated cleavage of certain sulfur-nitrogen containing compounds, preferably a cyclic 1,3-sulfur nitrogen ring system, and most preferably a thiazolidine compound. For convenience, these compounds may be referred to as "image dye-releasing thiazolidines". The same release mechanism is used for all three image dyes, and, as will be readily apparent, the image dye-forming system is not redox controlled.
A technique which utilizes two different imaging mechanisms, namely dye developers and image dye-releasing thiazolidines, is described and claimed in U.S. Pat. No. 4,740,448. According to this process the image dye positioned the greatest distance from the image-receiving layer is a dye developer and the image dye positioned closest to the image-receiving layer is provided by an image dye-releasing thiazolidine. The other image dye-providing material may be either a dye developer or an image dye-releasing thiazolidine.
In multicolor dye developer transfer processes, it has been recognized that, for example, less magenta density may be present in the transfer image than one would have predicted where there has been blue exposure but no green exposure, i.e., some magenta dye developer did not transfer even though there was no exposed green-sensitive silver halide to control its transfer. This problem is sometimes referred to as "magenta dropoff" and is believed to be the result of oxidation of the magenta dye developer as a result of the development of exposed blue-sensitive silver halide (rather than green-sensitive silver halide), the magenta dye developer being oxidized either directly or by an electron transfer redox reaction with oxidized messenger developer oxidized by exposed blue-sensitive silver halide. This undesired reaction is, at least in major part, because the magenta dye developer has to diffuse through the blue-sensitive silver halide layer to reach the image-receiving layer. In addition, the possibility has been recognized that yellow dye developer may be immobilized by development of green-sensitive silver halide, giving a different kind of crosstalk resulting in reduced yellow transfer density and increased magenta transfer density. Analogous situations may occur between the magenta and cyan dye developers. Such undesired interactions reduce color saturation and color separation and accuracy in the final image.
The photographic system taught by U.S. Pat. No. 4,740,448 reduces substantially the problem of crosstalk between adjacent silver halide emulsion layers in the formation of their respective imagewise distributions of diffusible image dyes. However, this phenomenon continues to occur in multicolor diffusion transfer photographic films such as those which utilize dye developers to provide the requisite imagewise distributions of diffusible cyan, magenta and yellow image dyes and also may occur to some extent in films which utilize dye developers together with thiazolidine image dye-providing materials dependent upon the particular photographic materials employed. It would be desirable to provide a multicolor diffusion transfer photographic film wherein such undesired interactions can be reduced substantially or virtually eliminated.
As the state of the art advances, novel approaches continue to be sought in order to attain the required performance criteria for these systems. Accordingly, investigations continue to be pursued to provide such beneficial effects. The present invention relates to novel photographic systems.